Re: [Xen-devel] [XTF PATCH] build: disable PIE during linking if necessary

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 01/02/17 16:21, Wei Liu wrote:
> Starting from ee3e265688, $(CC) is used for linking. That means all
> default $(CC) flags coming from distro takes effect.
>
> On Debian Stretch, gcc contains -pie by default, which makes the final
> object fail to link. We need to explicitly disable PIE when linking.
> Since not all versions of gcc support -no-pie, test its availability
> before adding.
>
> Example error message:
>
> /usr/bin/ld: /local/work/xtf.git/arch/x86/boot/head_pv64.o: relocation 
> R_X86_64_32S against symbol `start_info' can not be used when making a shared 
> object;
> recompile with -fPIC
> /usr/bin/ld: /local/work/xtf.git/arch/x86/entry_64-pv64.o: relocation 
> R_X86_64_32S against `.text' can not be used when making a shared object; 
> recompile with
> -fPIC
> /usr/bin/ld: final link failed: Nonrepresentable section on output
> collect2: error: ld returned 1 exit status
>
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>

LGTM.  Any objection if I s/DISABLE_PIE_LDFLAGS/COMMON_LDFLAGS/ on
commit? I don't think the name needs to be that specific.

~Andrew

> ---
>  build/common.mk | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/build/common.mk b/build/common.mk
> index 7c4870e..8e08c7e 100644
> --- a/build/common.mk
> +++ b/build/common.mk
> @@ -50,6 +50,15 @@ obj-perarch :=
>  obj-perenv  :=
>  include $(ROOT)/build/files.mk
>  
> +
> +cc-option = $(shell if [ -z "`echo 'int p=1;' | $(CC) $(1) -S -o /dev/null 
> -x c - 2>&1`" ]; \
> +                     then echo y; else echo n; fi)
> +
> +# Disable PIE, but need to check if compiler supports it
> +ifeq ($(call cc-option,-no-pie),y)
> +DISABLE_PIE_LDFLAGS := -no-pie
> +endif
> +
>  # Run once per environment to set up some common bits & pieces
>  define PERENV_setup
>  
> @@ -61,7 +70,7 @@ CFLAGS_$(1) := $$(CFLAGS_$($(1)_arch)) 
> $$(COMMON_CFLAGS-$(1)) -DCONFIG_ENV_$(1)
>  
>  link-$(1) := $(ROOT)/arch/x86/link-$(1).lds
>  
> -LDFLAGS_$(1) := -Wl,-T,$$(link-$(1)) -nostdlib
> +LDFLAGS_$(1) := -Wl,-T,$$(link-$(1)) -nostdlib $(DISABLE_PIE_LDFLAGS)
>  
>  # Needs to pick up test-provided obj-perenv and obj-perarch
>  DEPS-$(1) = $(head-$(1)) \


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